Technicaland Theoretical Research On Nanosecond Laser Peen Forming Of Metallic Sheets

Laser peen forming is one of the applications of laser shock wave technology.It has many advantages,such as non-contact,tool-free and high efficiency.It can also induce compressive stress on the target,which is desirable for resisting cracks from corrosion and fatigue.Therefore,laser peen forming has received more and more attentions due to its advantages.In this paper,the technical rules of single-curvature bending sheets and S-shaped double-curvature bending sheets of 2024 aluminum alloys were investigated through laser peen forming,the forming methods of S-shaped bending sheets were analyzed,the three-dimensional distortion part was obtained through laser peen forming in experiment,and the analytical curvature expression of bending sheets formed by laser peen forming was studied through theoretical research.The main contents and conclusions are as follows:(1)Numerical study on the technical rules of single-curvature parts of 2024 aluminum alloys with ABAQUS software has been conducted.The influence of different process parameters of laser peen forming,such as laser pulse energy,sheet thickness,shock area and coverage rate,on single-curvature parts were investigated.The results show that when the laser energy is certain the sheet is more likely to be concave bending with thin sheets and to be convex bending with thick sheets.The results also show that increasing shock area or coverage rate,will increase the deformation amount of bending sheet,but will not change the bending direction.(2)Experimental study on the technical rules of 2024 aluminum alloys through laser peen forming has been conducted.The influence of different process parameters,such as laser pulse energy,sheet thickness,shock area and coverage rate,on single-curvature bending sheets and S-shaped double-curvature bending sheets were investigated.The forming methods of S-shaped parts were analyzed.The three-dimensional distortion part was obtained through laser peen forming in experiment.The results show that the technical rules of forming S-shaped bending sheets are the same with that of single-curvature bending sheets.The results also show that the deformation amount of two different shock zone of S-shaped bending sheetsthrough laser peen forming is basically the same with the same process parameters.(3)The study on analytical curvature expression of bending sheets after laser peen forming has been conducted.Based on the internal force and internal moment balance equation,the analytical model for convex bending was established on the condition that the stress gradient mechanism dominates the forming process.Based on the principle of energy conversion,the analytical model for concave bending was established on the condition that the shock bending mechanism dominates the forming process.The coupling effect of stress gradient mechanism and shock bending mechanism was taken into consideration,and the final analytical curvature expression was given.The calculation precision of the analytical expression was validated by experiments.The results show that the analytical expression can be used to predict the changing trend of bending curvature with increasing laser energy on the condition that the stress gradient mechanism completely dominates the forming process,and the analytical expression can be used to predict the changing trend of bending curvature with increasing laser energy on the condition that the shock bending mechanism completely dominates the forming process.It can be found that oversimplification of the analytical model is an important reason for the deviation of analytical curvature and experimental curvature.